This invention relates generally to a finger identification and finger image processing apparatus. More particularly it relates to apparatus and method for encoding finger image information into machine readable signals with apparatus that is simple, inexpensive and reliable.
There are a number of systems that have been proposed for the processing of identification information based on the unique configuration of ridges and valleys in an individual's finger. When such information is taken from an ink impression of an individual's finger it is normally called a fingerprint. The more sophisticated techniques that employ optical techniques tend to provide a more refined, discriminate and accurate identification image; which image applicant has frequently called a fingerpress in order to distinguish it from the more primitive ink fingerprint. However, since both are based on the same unique ridge and valley finger characteristics, it should be understood that the term fingerprint is used by applicant generically. The term fingerprint object is used to refer to the actual configuration of the ridges and valleys of the finger when pressed against a surface. The term fingerprint image refers to the image of the fingerprint object that is obtained by using an optical system. In these optical systems, the finger of the subject individual is placed against the back of a transparent platen and the normally flat fingerprint object on the back surface of the platen is imaged through the front of the platen and projected as a fingerprint image onto receiving or processing equipment. This receiving equipment may take the form of a screen, a camera or an array of photocells.
For example, U.S. Pat. No. 3,138,059 discloses such a system. As described in the '059 patent, the finger is pressed against a transparent platen and a light beam is projected against the platen. Light is reflected from the finger to a recorder in the form of a camera. U.S. Pat. No. 4,053,228, issued on Oct. 11, 1977 discloses a holographic identification system the disclosure of which is incorporated herein by reference. As described in the '228 patent, a collimated, coherent light beam is projected against the front surface of a transparent platen. The light is reflected from the back surface of the platen, against which surface the subject's finger is pressed. The reflected light beam is modulated with the finger image and is correlated against a hologram of the same fingerpress to provide indentification.
However, systems of this type suffer from a number of disadvantages, foremost among which is a high degree of inaccuracy. That is, mismatching can easily occur between the hologram and the image. Mismatching error is reduced by employing accurate alignment procedures but this solution increases the cost and complexity of the system. Aside from the question of alignment apparatus, such systems are extremely expensive as they require beam splitters, devices to change direction of the light beams, focusing lenses, devices to effect the necessary correlations, etc. Additionally, these systems are difficult to maintain and service because of the number of elements comprising the systems and the fact that even the slightest vibration can knock a lens or a mirror out of position.
Accordingly, it is a major purpose of this invention to provide a technique for processing a fingerprint or fingerprint object in a fashion that is simple and unambiguous, that avoids undue messiness, provides a high degree of reliability in operation and that can be implemented in equipment which is relatively trouble free and that requires a minimum of maintenance.
It is a further object of this system to provide an accurate and unambiguous fingerprint image which in turn is susceptible to being encoded into machine readable signals.
In the holographic systems, stringent requirements are placed on the platen. The surfaces of the platen must be completely flat to minimize inaccuracies introduced into the reflected light beam. In general, where a lot of light is lost and where the contrast between the ridges and valleys in the image is low, the platen must be an expensive precision unit.
In addition, build up of finger oil introduces inaccuracies into the system. Often, a latent image is fixed to the platen by the finger oil residue on the platen. The operator must maintain the platen clean by wiping it after each use. However, even if the platen is clean, these systems are sensitive to either too much or too little oil from the finger. Either case may produce erroneous results. Other problems occur when the platen is cold and a warm finger is placed against it. This fogs the platen. While a platen may be preheated to eliminate this problem, such a solution is impractical.
Accordingly, a further object of this invention is to provide a highly accurate and reliable finger identification and processing apparatus that includes a relatively inexpensive platen.
Another object of the invention is to provide a finger receiving platen, for such an apparatus, that is insensitive to the amount of oil on a finger.
A further object of the invention is to provide optical fingerprint processing apparatus with greatly enhanced optical contrast between the valley zones and the ridge zones of the finger image.
Another object of the invention is to provide an optical scanning system which minimizes optical distortion, requires a minimum of optical components, and can be used for scanning of a fingerprint object on a platen as well as the scanning of a fingerprint image on a card.
A further object of this invention is to provide a system which is adapted to be used for both verification and identification. Verification is required in access control. Identification is required in police work.